Despite its widespread use, the clinical utility of doxorubicin (DOX) is specifically compromised by dose-limiting cardiotoxicities. Currently approved therapy (dexrazoxane) has only modest value in adults and its usefulness in children for cardiac protection is still being investigated. Efficacy of DOX also seems to be reduced during dexrazoxane co-administration; this lack of selective protection of heart muscle discourages its clinical use. We have demonstrated first-time evidence of cardiac formation of peroxynitrite, NOS2 induction, and oxidative injury to key components of cardiomyocyte metabolism/energetics during DOX cardiomyopathy. We have identified a mixture of agents that provided remarkable protection of cardiac myocytes in vitro with no effect on DOX induced cancer cell killing. Their components are each known to be safe, and their combination provided unique protective value. We will test this approach in vivo, using two established and reliable rodent models of cancer relevant to DOX clinical use (breast cancer model and leukemia models). Our AIMS are: (1) Evaluate the safety of the identified infusion solution in mice and demonstrate protection from DOX induced cardiac dysfunction in vivo; (2) Demonstrate proof of principle for selective cardioprotection with no effect on DOX tumoricidal actions in a mouse model of breast cancer tumor progression; (3) Demonstrate selective effects for myocardial protection in an in vivo mouse model of childhood leukemia. Phase I endpoints include the demonstration of a safe infusion solution that provides specific protection of cardiac tissue from DOX injury and dysfunction without impairing DOX tumoricidal actions in vivo. Despite its widespread use, the clinical utility of doxorubicin (DOX) is specifically compromised by dose-limiting cardiotoxicities while currently approved therapy (dexrazoxane) has only modest value in adults and its usefulness in children for cardiac protection is still being investigated. We have identified a mixture of agents that provided remarkable protection of cardiac myocytes in vitro with no effect on DOX induced cancer cell killing. We will test this approach in vivo, using two established and reliable rodent models of cancer relevant to DOX clinical use (breast cancer model and leukemia models). [unreadable] [unreadable] [unreadable]